This invention relates generally to mechanical fasteners and, more particularly, to retainer's for fastening compression die springs in their respective spring pockets. The invention may be utilized with compression die springs of any spring stock cross section configuration.
In Tool & Die assemblies, compression springs are used to either provide holding pressure while forming the part or stripping the part from the trim or form punch. The compression spring is positioned in a cylindrical opening drilled in a die, known as a "spring pocket." The spring applies a bias to a member called a "pad" or "stripper." When such pad or stripper is removed from an upper die member, the compression springs will drop out of the spring pockets under the influence of gravity unless retained in the pockets by retainers.
Various forms of spring retainers have been proposed to retain the compression springs in the spring pockets of the upper die member when the pad or stripper is removed. Prior art die spring retainers typically utilize a socket head cap screw, or a shoulder screw, to hold a retainer and, thus, the compression spring in place. This requires drilling and tapping of a tack hole in the bottom of the spring pocket and a relatively complex maneuver in order to assemble the spring, retainer and fastener into the spring pocket and provides a retention force greatly in excess of that required. While such prior art spring retainers are effective, they add significant cost to the die assembly.
In order to retain a compression spring in the spring pocket of an upper die member, it is necessary only to provide a retention force that equals the weight of the spring plus an engineering safety factor. Because even heavy-duty and extra heavy-duty compression die springs weigh on the order of magnitude of a pound, the force required to retain a die spring in a spring pocket is not great.